Accelerometers have been used in airborne navigation systems in the past, but only in conjunction with gyros. The current route guidance and navigation systems that exist for automobiles today use the vehicle speed signal, rate gyro and a reverse gear hookup to "dead reckon" the vehicle position from a previously known position. This method of dead reckoning, however, is susceptible to sensor error, and therefore requires more expensive sensors for accuracy and dependability.
The systems that use odometers, gyros and reverse gear hookups also lack portability due to the required connections to odometers and the frailty of gyros. Moreover, these systems are hard to install in different cars due to differing odometer configurations which can have different connections and pulse counts in the transmission. Odometer data also varies with temp, load weight, tire pressure, speed. Alternative connections to cruise control or ABS sensors bring up safety concerns. This reduces the installation flexibility, increases installation costs and reduces the portability of the vehicle navigation system. Accordingly, there is a need for a vehicle navigation system with more freedom of installation which is portable and accurately determines vehicle position.